Superconducting Gap Function in Antiferromagnetic Heavy-Fermion UPd_2Al_3 Probed by Angle Resolved Magnetothermal Transport Measurements

TL;DR

This study investigates the superconducting gap structure of UPd_2Al_3, revealing a d-wave symmetry with a single line node orthogonal to the c-axis, using angle-resolved magnetothermal transport measurements.

Contribution

It provides the first direct experimental evidence of the gap node structure in UPd_2Al_3, linking it to its antiferromagnetic order and resonance features.

Findings

Gap function has a single line node orthogonal to the c-axis.

Gap is isotropic within the basal plane.

Consistent with neutron scattering resonance peak.

Abstract

The superconducting gap structure of heavy fermion UPd_2Al_3, in which unconventional superconductivity coexists with antiferromagnetic (AF) order with atomic size local moments, was investigated by the thermal conductivity measurements in a magnetic field rotating in various directions relative to the crystal axes. The results provide strong evidence that the gap function \Delta(k) has a single line node orthogonal to the c-axis located at the AF Brillouin zone boundary, while \Delta(k) is isotropic within the basal plane. The determined nodal structure is compatible with the resonance peak in the dynamical susceptibility observed in neutron inelastic scattering experiments. Based on these results, we conclude that the superconducting pairing function of UPd_2Al_3 is most likely to be d-wave with a form \Delta(k)=\Delta_0 cos(k_zc)